A known vehicle motion control apparatus is disclosed in JP11-227586A. When an operation such as lane changing is conducted rapidly to avoid a certain danger, the motion control apparatus calculates a deviation between a target yaw rate, which is calculated based on a steering angle determined by the steering operation of the driver, and an actual yaw rate, which is detected based on the yaw rate sensor. Then, the motion control apparatus determines a state of a vehicle skid based on the deviation. In case that a skid occurs, a pump supplies the brake fluid for applying a braking force to outer wheels relative to the turning direction, i.e. the wheels to be controlled (hereinafter, referred to as the controlled wheel). Thus, the braking force is applied independently from the brake operation of the driver.
After turning the steering wheel back in a reverse direction during the lane changing, a large skid may occur while the vehicle is turning in the reverse direction.
In order to improve the responsiveness of the braking force applied to the wheels for suppressing the large skid which may occur after turning the steering wheel back, the motion control apparatus applies a pressure preload to a front wheel, which is located at a horizontally opposite side of the outer wheels, i.e. the controlled wheel, to eliminate a clearance around the wheel cylinder.
However, in the preload operated by the motion control apparatus disclosed in JP 11-227586A, the fluid pressure, which is not large enough to generate the braking force for the wheel, is provided as the preload. Thus, after turning the steering wheel back in the reverse direction, the occurrence of the skid is not suppressed.
A need exists for a vehicle motion control apparatus which suppresses an occurrence of a skid in a direction that a steering wheel is turned back, when the steering wheel is turned back in lane changing.